This invention relates to shipboard navigation lights for preventing collision at sea, and more particularly to an improved, high intensity, submersible, running light fixture.
Shipboard running lights have generally comprised an electric incandescent lamp housed in a fixture including a lens or globe of colored glass that transmits light of a particular hue or color through a predetermined azimuth sector relative to the head of the vessel. The color, range of visibility, and sector of the lights are stipulated in international rules. Recent changes in the rules have been adopted that require considerably greater visual range of lights and specify candlepower output required for the range. The method used for computing the required output is very conservative and results in values approximately ten times higher than other accepted values.
Attempts to satisfy the new requirements by merely inserting lamps of higher wattage and intensity in existing lamp fixtures have not been satisfactory. In the use of existing port running light fixtures using a red glass globe, for example, the increase in wattage results in considerable increases in operating temperature of the globe, leading to globe fracture upon cooling and, because the percent of light transmittance of the globe is materially decreased with increases in temperature, the required range of visibility is not met. Moreover, increases in operating temperatures are accompanied by shifts in chromaticity of glass globes. In the case of existing green globes that shift is toward the yellow region, and can render the fixtures unacceptable under the new rules. Red glass globes present the greatest challenge because of the great reduction in transmittance that occurs with increases in temperature.
In some arts using high intensity lamp fixtures, it is practical to carry away excess heat by means for ventilating the fixture, forced circulation of a cooling medium, or the like. Shipboard navigation lights, however, are often subjected to spray or immersion. Those intended for use on naval vessels such as submarines are required to withstand submergence to great depths and must be so sealed against water intrusion and free of auxiliary mechanisms that cooling by ventilation or forced circulation of a cooling medium become impractical.